Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite or admit an air and fuel mixture to produce heat. In one example, fuel directed into a combustion chamber of the engine can be ignited by way of a spark plug. The heat and expanding gases resulting from this combustion process are directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation is then utilized to drive a device such as a transmission or a generator to propel a vehicle or to produce electrical power.
During operation of the engine described above, a complex mixture of air pollutants is produced as a byproduct of the combustion process. These air pollutants are composed of solid particulate matter and gaseous compounds including nitrous oxides (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of solid particulate matter and gaseous compounds emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to reduce the production of these pollutants is to introduce a lean air/fuel mixture into the combustion chambers of the engine. This lean mixture, when ignited, burns at a relatively low temperature. The lowered combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of regulated emission constituents. As emission regulations become stricter, leaner and leaner mixtures are being implemented.
Although successful at reducing emissions, very lean air/fuel mixtures are difficult to ignite. That is, the single point arc from a conventional spark plug may be insufficient to initiate and/or maintain combustion of a mixture that has little fuel (compared to the amount of air present). As a result, the emission reduction available from a typical spark-ignited engine operated in a lean mode may be limited.
One attempt at improving combustion initiation of a lean air/fuel mixture is described in U.S. Pat. No. 8,104,444 (the '444 patent) issued to Schultz on Jan. 31, 2012. The '444 patent discloses an igniter including a body and a pre-combustion chamber integral with the body and having at least one orifice. The igniter also includes at least one electrode associated with the pre-combustion chamber. The at least one electrode is configured to direct high frequency electromagnetic energy (RF energy) to lower an ignition breakdown voltage requirement of an air and fuel mixture in the pre-combustion chamber. The at least one electrode is also configured to generate an arc that extends to an internal wall of the pre-combustion chamber and ignites the air and fuel mixture. The use of RF energy may facilitate combustion of a lean air and fuel mixture in a main combustion chamber.
Although the igniter of the '444 patent helps to provide a more consistent and reliable combustion, improvements may still be possible. Specifically, the air and fuel mixture in the pre-combustion chamber of the '444 patent could be leaner, which would further reduce the formation of regulated emission constituents.
The disclosed ignition system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.